One known type of steering apparatus of a vehicle is a rack-and-pinion steering apparatus in which a rotational force and an amount of rotation of a pinion are converted into a thrust in the axial direction and a stroke of a rack shaft by meshing engagement of the rack teeth of the rack shaft with the pinion. Here, in some of rack holding mechanisms for holding a rack, the transmission efficiency has been improved, and the steering torque has been reduced by providing a rolling rack guide, etc., which can support the rack by a roller, etc., rotating at a holding part for holding the back surface (the opposite side of the rack teeth) of the rack shaft.
At the same time, a so-called Y-type rack shaft, which is produced by forging to have a Y-type (shaped) section orthogonal to the axis line, has been developed in order to improve the strength of the rack teeth. An example, in which such a Y-type rack shaft and the rolling rack guide described above are applied to a steering apparatus, is shown in FIG. 4. In FIG. 4, an output shaft 3 extending horizontally in a housing 1 is connected to an unillustrated steering shaft, and rotatably supported by bearings 5, 6 with respect to the housing 1. The inner ring of the bearing 6 is fixed to the end of the output shaft 3 by a nut 8, and the outer ring of the bearing 6 is attached to the housing 1 by screwing a fixing member 9, which also serves as a cover member.
The housing 1 is provided with a hollow columnar portion 1c formed from the circumference of the rack shaft 10, which is a Y-type rack shaft, extending upward in the figure. A supporting unit 20 is disposed in the hollow columnar portion 1c. The supporting unit 20 includes a substantially cylindrical holder 21, a pin 22 contained in a groove 21a of the holder 21, a roller 24 rotatably supported by a bearing 23 with respect to the pin 22, a pipe-shaped screw member 25 for attaching the holder 21 to the hollow columnar portion 1c, a disc spring 24A disposed between the holder 21 and the screw member 25 for urging the holder 21 to the rack shaft 10 against the screw member 25, and a lock member 26 of the screw member 25.
The rack shaft 10 has a pair of slanted surfaces 10c, 10c on both sides across a cylindrical surface 10b provided on the opposite side of rack teeth 10a in mesh with a pinion 3a of the output shaft 3. The roller 24 has an integral structure connecting a pair of truncated cones 24a, 24a by a cylindrical portion 24b. The truncated cones 24a, 24a are disposed rotatably along the slanted surfaces 10c, 10c of the rack shaft 10, respectively, thereby having a function of restraining a rotational displacement of the rack shaft 10.
Here, when a strong force is transmitted between the output shaft 3 and the rack shaft 10, such a force is supported by the supporting unit 20. Since the roller 24 has a structure described above, the slanted surfaces 10c, 10c of the rack shaft 10 enters into the truncated cones 24a, 24a and acts so as to push and spread them by a so-called wedge action. Thus, the truncated cones 24a, 24a deform as shown by the dotted line in the figure, thereby disadvantageously hindering the smooth rotation. To cope with this, an increase in the rigidity of the roller 24 can be considered in order to restrain the deformation of the truncated cones 24a, 24a. However, in order to restrain the deformation against the wedge action, it is necessary to construct the roller 24 to be considerably strong. Thus, there is a problem in that the entire steering apparatus becomes large and heavy.
The present invention has been made in view of the problems of these conventional techniques, and it is an object of the present invention to provide a steering apparatus having a light-weight and compact configuration and capable of supporting the Y-type rack shaft more appropriately.
In order to achieve the above object, according to the present invention, there is provided a steering apparatus including:
a housing; a rack shaft connected to a steering mechanism, having rack teeth formed at least on part of an outer surface, and movably supported with respect to the housing; and a pinion connected to a steering wheel and having meshing engagement with the rack teeth,
wherein the rack shaft is provided with a rolling contact surface on the opposite side of the rack teeth across an axis line and a pair of surfaces extending in parallel with an axis line on both sides across the rolling contact surface,
the apparatus further comprises a rolling member rolling on the rolling contact surface of the rack shaft and an urging member having contact with the pair of surfaces and applying an urging force,
wherein the urging member is attached to the housing, forms an annular configuration surrounding the entire circumference of the rack shaft, and has a contact portion having contact with the pair of surfaces to apply an urging force.
By the steering apparatus according to the present invention, in the steering apparatus including: a housing; a rack shaft connected to a steering mechanism, having rack teeth formed at least on part of an outer surface, and movably supported with respect to the housing; and a pinion connected to a steering wheel and having meshing engagement with the rack teeth, the rack shaft is provided with a rolling contact surface on the opposite side of the rack teeth across an axis line and a pair of surfaces extending in parallel with an axis line on both sides across the rolling contact surface. Furthermore, the apparatus includes a rolling member rolling on the rolling contact surface of the rack shaft and an urging member having contact with the pair of surfaces and applying an urging force, wherein the urging member is attached to the housing, forms an annular configuration surrounding the entire circumference of the rack shaft, and has a contact portion having contact with the pair of surfaces to apply an urging force. Therefore, the force exerted on the rack shaft by the pinion can be supported by the rolling member contacting with the rolling contact surface. Moreover, it is possible to restrain a rotational displacement of the rack shaft about the axis line by applying the urging force against the pair of surfaces of the rack shaft by the contacting portion of the urging member. Also, since the urging member has an annular configuration, it is advantageously possible to easily attach/detach the urging member to/from the housing without using a connecting member such as adhesive or a screw.
Furthermore, the contact portion of the urging member preferably includes a pressing portion having the shape of a cantilever.